Internal suspended insulating ceiling for storage tanks

ABSTRACT

1,153,602. Liquefied gas storage containers. CHICAGO BRIDGE &amp; IRON CO. 19 Oct., 1966 [15 Dec., 1965], No. 46837/66. Heading F4P. A liquefied gas storage container having an externally heat insulated metal base and a metal cylindrical side wall 50 has a fixed-position flat heat-insulated metal ceiling 63, 66 extending across the container and conforming at its periphery with the wall 50 above the highest liquid level; the ceiling being suspended from the metal roof 52 of the container, e.g. by three concentric circular courses A, B, C of spaced rods 61, 62. The roof 52 which is not insulated is formed of overlapping plates 53, 56, 57 and a peripheral ring 55. Flexible glass fibre insulation 67 is located between the container wall 50 and an L-sectioned metal ring 64 round the periphery of the ceiling. In a modification the insulated ceiling is supported on joists which are themselves suspended by rods from the roof.

Nov. 14, 1967 s. E. SATTELBERG ET AL 3,352,443

INTERNAL SUSPENDED INSULATING CEILING FOR STORAGE TANKS 15, 1965 Filed Deo.

5 Sheets-Sheet l Nov. 14, 1967 S. E. SATTELBERG ET AL INTERNAL SUSPENDED INSULATING CEILING FOR STORAGE TANKS Filed Dec. l5, 1965 ,9x27 Z M414 v ATTORNEYS NOV. 14, 1967l 5 E SATTELBERG ET AL 3,352,443

INTERNAL SUSPENDD yINSULATING kCEILING FOR STORAGE TANKS .Filed Dec. 15, 1965 5 Sheets-Sheet 5 55 57 52X 53 54 l" a 59 260 53 ,I 59 58 -c 58 55 KB /NVENTORS huw] .Zg f @u United States Patent 3,352,443 INTERNAL SUSPENDED INSULATING CEILING FOR STORAGE TANKS Stanley E. Sattelberg, Naperville, and Yuksel A. Selcukoglu, Chicago, lll., assignors to Chicago Bridge & Iron Company, Oak Brook, Ill., a corporation of Illinois Filed Dec. 15, 1965, Ser. No. 514,029 17 Claims. (Cl. 220-9) This invention -relates to insulated storage tanks where heat gain or loss is a problem. More particularly, this invention is concerned with improved tanks which have low heat-leak and heat-input characteristics and which are more economical to construct than many other tanks of comparable size and which are so constructed as to have a more trouble-free service life. The invention is especially suitable for refrigerated storage tanks, such as for storing liqueed gases.

Tanks are used to store various liquid and solid materials. Although many materials can be suitably stored at prevailing ambient temperatures, it is often advisable, and sometimes necessary, that products be stored in tanks at temperatures which differ significantly from existing ambient temperatures. Because of this, insulated storage tanks have been used to maintain solid or liquid products at lower and higher temperatures than ambient temperature, i.e., to keep heat in or out of the tank.

Insulated storage tanks are generally an enclosed met-al shell having such insulation thereon as to reduce heat transfer to the extent considered practical. Such tanks can be used to store edible materials such as grains and oils where temperature control of the product is advantageous, as well as liquid petroleum products of all types.

A number of gases are stored in liqueed condition in insulated tanks. Among these gases are hydrogen, nitrogen,'oxygen, methane (natur-al gas), ethylene and propane. One type of tank for storing such gases in liqueed form is comprised of an enclosed metal shell, usually of metal plate, which remains ductile at the extremely low temperatures at which the liqueiied gas is stored.

The tanks store the liquefied gas -at a temperature which maintains it liquid at about, or slightly above, atmospheric pressure. It is more economical to store liqueed gases at such pressures because of the increased cost of making large tanks or vessels strong enough to hold the liquefied gas at higher temperatu-res and pressures.

The tank shell comprises a flat metal bottom to which is secured a metal wall, usually cylindrical in shape, and joined to and supported by the Wall is placed a metal roof usually dome-shaped, although it can be ellipsoidal, cone-shaped or some other shape. In such tanks, the bottom, Wall and roof are insulated to reduce heat-leak suiciently to obtain practical conditions of storage for a liquefied gas. The bottom and wall insulation generally presents no special problem of installation or maintenance because the bottom surface is flat and the wall cylindrical of large radius so panels or blocks of insulation can generally be applied easily. Insulating the roof, however, is a different problem because of its shape. Whether it is a spherical, ellipsoidal or conical dome, pre-assembled insulation panels or precast blocks cannot readily be itted on the outside of the roof. In addition to the installation problem, all external roof insulation, which is the conventional Way of insulating such tanks, is exposed to the weathering action of sun, rain, snow and ice and temperature extremes due to weather changes, as well as the mechanical forces and movements associated with weather and operating conditions. The roof insulation life is thus often short and maintenance high as compared to the more easily applied and better protected insulation on the vertical, cylindrical walls of the tank, and the insulated bottom which is inherently protected.

3,352,443 Patented Nov. 14, 1967 ICC In order to overcome or avoid shortcomings involved with prior storage tanks, there is provided by this invention an improved, enclosed, insulated tank for storing solid and liquid materials at temperatures above land below ambient temperature, including liqueed gases, such as stored at about atmospheric pressure. The tank has an enclosed metal shell having -a metal bottom, a metal wall and a metal roof, with both the bottom and wall being insulated adequately to suitably retard heatleak or heat-input. The area surrounded by the wall is enclosed by a roof which for practicing this invention is advisably of noninsulating metal plate but which can, if desired, be insulated. The improved liquid storage tank has an insulated, advisably fixed-position ceiling suspended from the roof by suitable means. The periphery of the insulated suspended ceiling conforms at least approximately to the inside horizontal shape of the tank wall.

Although the ceiling can contact the inside wall surface, there is advisably clearance provided between them. Such clearance is useful when the tank contains a liquid product or liquefied gas product so that vapor transmission can be effected by means of such clearance from below the ceiling to the space above it and from the space above the ceiling to the space below it. Vapor transmission to and from the spaces above and below the ceiling alternatively can be effected -by suitable ports provided in the suspended ceiling or by a ceiling which is not gas tight. Vapor transmission 'between such spaces prevents creation of a pressure differential between such spaces from heat-leak, heat-input or such as by flashingV of ya liquid cryogen into the tank during lilling, or emptying, which could cause damaging forces on the ceiling.

In -order further to illustrate and describe the invention, it will be discussed further in conjunction with the attached drawings in which: I

FIGURE 1 is a vertical section through an enclosed insulated storage tank, having a suspended insulating ceiling according to one embodiment of this invention;

FIGURE 2 is a horizontal section, partially broken away, through the tank wall of FIG. 1 above the upper surface of the ceiling;

FIGURE 3 is an enlarged, vertical, sectional view taken at line 3-3 of FIG. 2, showing structural detail of the insulated suspended ceiling;

FIGURE 4 is -a horizontal, sectional view taken at the line 4 4 in FIG. 3;

FIGURE 5 is a vertical, sectional view on the line 5--5 of FIG. 2 and shows the structure used for supporting the abutting ends of joists used in the ceiling assembly;

FIGURE 6 is a vertical, sectional view on the line 6-6 of FIG. 2 and shows cross-bridging used to stitfen the joists;

FIGURE 7 is a vertical, sectional view showingvthe rafter means used for distributing the load of the suspended ceiling of FIG. l over the Iroof area;

FIGURE 8 is a horizontal section, partially broken away, through a tank wall above the upper surface of another embodiment of the insulated ceiling; and

FIGURE 9 is a partial vertical section through an enclosed insulated storage tank and shows structural dctail for the same insulated suspended ceiling embodiment shown in FIG. 8.

In the drawings, the same number is used to identify the same structural element wherever it appears.

With reference to FIG. l, a supporting foundation V1t), such as of concrete, is set into the earth as a foundation and on top of it is placed insulating material 11 of a suitable thickness and which is capable of bearing the combined load of the tank and its contents when iilled. On top of insulation 11 is placed a metal bottom 12 to which tank wall 13 is secured at the bottom edge, such as by Welding. The wall 13v is advisably cylindrical. The external surface of wall 132 is provided with insulation 14 of suflicient thickness to retard heat-leak or heat-input enough to permit practical storage of a product in the tank. Enclosing tankV wall 13 is roof 15 which is domeshaped. A peripheral ring portion 16, of thicker metal plate than the upper portion 17 of the roof, is provided to strengthen the roof and stiien the wall and support the ends' of, rafters 18 reinforcing the roof as shown in FIGS. 3, and 7. Rafters 18 follow the internal contour of the roof. The rafters are advisably metal angles as in FIG. 7. Rafters 18 need not be used when the plates are made thick enough to carry the load without stiffening.

Connected to the bottom of the rafters 18, or directly to the roof plate, and running approximately normal to the radial rafters are load-distributing members 19, as shown in FIGS. 5 and 7, which more or less conform to the contour of the roof. Fastened at spaced apart locations on the load-distributing members 19 are plates 20 asshown in FIG. 5, from which elongated suspending members 21 hang vertically downward to support member 22 to which it is connected such as by welding. The members 22, as shown in FIG. l, run parallel to each other throughout the width of the tank.

Between adjacent, parallel supporting members 22 is positioned a conventional open web bar joist 23, or other lightweight structural member which is supported at each end by adjacent members 22, except for the ends of the joist in proximity to the tank wall 13. The ends of the joists 23 adjacent the tank wall are supported by plate 24, as shown in FIG. 3, which is connected to member 25. The supporting elongated member 26, similar to` members 21, is connected at its lower endto member 25 and at its upper end to plate 27 which is connected to the lower surface ofthe roof ring 16. The member 25 formsl a' ring which extends around the ceiling edge although the ceiling periphery extends slightly further to aboutkthe tank wall. I

Y The open web bar joists 23 arecomposed of bar 28, as shown in FIG. 3, which is bent into a series of W shapes., and is aixed between top cord memberV 29, which is essentially U-shaped, and lower cordl member 30, which is also U-shaped, as shown'in FIG. 6. Joining upper cord 29 and lower cord 30 at theend ofthe joist is rod 31 as shown in FIG. 3. Member 3-2v is placed at the endof ,thel joist and is Vconnected at the lower side of the upper cord 29. The member 32 islessentilallylike the lower cord 30 in cross-sectionand provides a foot area for resting the end of the joist on bearing surface 24.

In order .to stiffen thejoists, which are arranged in parallel lines extending across the vessel, bridging, adyisablly of bar stock, can lbe run in parallel rows normal totherjoists to connect the lower cordstl. Thus, in FIG. 6, bar 33 can be extended from onel lower cord 30 to the lower cord of the next adjacent parallel joist. Furthermore, bar 34 can extenrlfrom the lower cord of a joist adjacent the tank wall 13 upwardly at an inclined angle to connect with member 25 as Yshown in FIG. 6. Member 25 forms aringhaving a diameter slightly less lthan the diameter o f the tank wall. Supportingthe circular memberZS at such location, in a manner similar to membrane 2 6, is elongated member 36.

Covering the joist network is decking 37, advisably of 'thertype whith'has channels running parallel to the side edges of the panels. The decking is shown in FIGS. l to 3 and 5. The decking 37 is placed normal to the joist and is ofV suflicient length to advisably span three or more joists. The decking has channeled areas 3S to provide rigidity and strength. The deckinglis advisably not run completely to the vessel wall. Expandable metal lath 39, as shown in FIG. A3, is formed to have a horizontal section and a vertical edge which is placed approximately in contact with the inside of the tank wall. The expandable metal lath 39 is secured to the top surface of the adjacent decking 37, such as by welding, and extends entirely 4 around the ceiling periphery. Instead` of` metal decking, decking of wood, plastic or other suitable materials can be used.

Any suitable insulation 39, which will reduce heat-leak or heat-inputv enough, can be placed on the upper surface of decking 37 in a thickness suicient to give the desired results. The insulation may be preformed andk blocks of suitable size positiontd in place on the decking, or loose insulation of the granular or occulent-type can be used. Furthermore, insulation of thefoam-type, such as polyurethane foam, can be foamed in place directlyY on the decking to provide the desired insulation 39.

FIGS. 8 and 9 illustrate another embodiment of the Y invention. Tank wall 50 of metal is externally insulated 51. The tank roof 52 is constructed of metal rings 53y which overlap at 54. A heavier metal plate ring 55 runs around the periphery of the roof and rests, on the top edge of wall 50. Metal plates 56 and 57 complete the roof shell, which is shown uninsulated.

A series of rafters 58, such asangle shapes, are axially connected to the underside of the roofV to reinforce it. The rafters can be made in sections and joinedby plates 59 to Z-ring girders 60 welded to the roof. Suspended from the girders 60 are rods 61. Similar rods 62 are suspended from the inner periphery of the roof and may be attached to the rafter ends as shown. Enough rods are employed to support the suspended ceiling. For a foot diameter tank about fifty to sixty rods are employed in the outer two circular courses A and B, having radii of about 48 and 28 feet respectively, and about fifteen to twenty rods in circular course C, having a diameter of about l5 feet.

The suspended ceiling is composed of flat sheet metal decking 63 fabricated from sheets of appropriate size Aand shape. FIG. 8 gives a representative arrangement of sheets and shapes used infabricating .the at ceiling. To support the flat ceiling sheet a com-pression rin'g64-is placed near about the periphery of the sheet. Only one such compression ring is necessary to supportthe at ceiling sheet. However, to provide further' reinforcing and to restrict sag of the sheet, one or more additional circular supporting rings 65 are provided. The suspension rods 61 and 62 are joined to compression ring 64 and supporting rings 65 to suspend the ceiling in fixed position. Insulation 66 is placed on the metal sheet 63- to a depth adequate for the purpose. The space between compression ring 64 and tank wall 50 is advisably insulated `67 by a material which is exible and somewhat porolls to permit vapor transmission. A blanket of glass Ifibers can be used for this purpose andit 'can 4be `supported by an outward projectingr lip 68 of the at metal sheet 63.V

Although all the drawings show y*the insulated ceiling substantiallyV planar and positioned lhorizontally inthe tank, it is within theV scopey of the invention to suspend the insulated ceiling in a conical, domed orother configuration. There is usually, howevenno advantage in such shapedsuspended insulating ceiling andfor most pur.: poses a planar, horizontallylsuspended ceiling -is satisfactory. Furthermore, the depth of the insulation layer on the decking or other means used-to support the insulation by the suspension system -can be of uniform thickness or the insulation thickness can be` increased at selected ceiling areas -if the heat-leak or heat-inputv isy greater in'vsuch areas than others. Thus, under certain conditions it might prove advisable to increase the depth of the insulation around the periphery of the insulated ceiling since there could be more heat-leak or heat-input at the uppenpart of the tank ywall than the central vpartof the'suspended ceiling.

'Fhe suspended ceiling is advisably located below the junction of the upper edge of the insulated wallA withthe outer edge of the roof. The metal Wall constitutes a direct path vfor heat to ow, such as from a warm. metal roof to a refrigerated liquid in the tank below theinsulated ceiling. Therportion ofthe metalv wall extendingvabove Vthe insulated ceiling is insulated. This prevents heat transfer and also 'prevents sweat and frost when the tank is to store a refrigerated liquid. Heat owing downward from the portion of the |Wall above the insulated ceiling, when the tank is used to store a cold product, is replaced by heat from the metal roof, heat from the stratifying warm gas above the suspended ceiling, and heat vfrom the outside air by heat-leak through the Wall insulation. The heat owing into the refrigerated, stored liquid through the path provided by the extension of the metal wall to the warm roof, although expected to be large, unexpectedly is small and insignificant. For example, in a 126 foot diameter refrigerated ammonia tank with ambient temperature at 110 F., this heat flow is equivalent to the normal heat-leak through a ring of normally insulated wall (5 in. foam glass on outside of 0.25 in. wall) only 1.4 feet high extending around the circumference of the tank. The reduction in temperature of the metal wall to roof junction, due to the heat flow through the extended shell with an ambient temperature of 110 F., is only 15 F.

This combination of an insulated suspended ceiling and an uninsulated roof provides an unusually suitable combination for storage of materials, Whether the product is to be kept below or above ambient temperature, because of the surprisingly low heat transfer through that portion of the tank wall above the insulated ceiling. Elimination of roof insulation, without sacricing efliciency, lowers the cost and provides a tank which can be expected to have a longer life with far less trouble than when the roof is externally insulated.

By extending the metal wall above the insulated ceiling, a controlled temperature gradient is achieved between the roof, Whether it be hotter or colder than the stored product, and the tank wall Iwhich is hot or cold according to the temperature of the stored product. This greatly increases the eiciency of the tank. Controlled heat-leak or heat-input renders the tank suitable for storage of -hot or cold products at temperatures much higher or lower than ambient temperature.

Although the most suitable position of the ceilin-g below the tank wall roof juncture is readily calculated precisely, it is usually suitable to place the ceiling about 1 to 3 feet below the said juncture in a tank to be used for storing a refrigerated liquid. For `storing other products, whether solid or liquid, where heat-input or heatleak is not as important, the ceiling can 'be placed even closer to the roof.

An important feature of this invention is the suspension means, particularly for large tanks, which distributes the weight or load of the ceiling over a substantial and perhaps, major part of the roof. This may be achieved by means of the rafters and/'or girders connected to the inside surface of the roof. Such structure prevents deformation of the roof which could otherwise likely result by simple attachment of the elongated suspending members 21 directly to a point on the inside surface of the roof. The combination of rafters and load-distributing members spreads t-he load lfrom the location of attachment of the elongated vertical members over most of the roof area.

It is also advisable that the suspended insulating ceiling be positioned in the tank to be above the full capacity level of the tank.

The provision of a suspended insulating ceiling in a tank for cryogenic storage permits the use of metals for the roof construction which are not adapted under other conditions for such purposes. The metal yused for the roof need not be one Which can withstand the refrigerated conditions to which the tank Walls and bottom are subjected because the roof is at no time cooled to anywhere near the temperatures of the tank wall and bottom during service. The roof operates at substantially ambient, instead of reigerated, temperature which allows the use of a less expensive roof material. This can result in sig- ,suspended in the tank above nificant cost reduction since more economical materialscan be used in the construction of `the roof than would be the case if the roof had to be constructed to withstand the refrigerated conditions encountered by the tank bottom and wall during storage such as of a cryogen liquid in the tank.

Various changes and modifications of the invention can be made and, to the extent that such variations incorporate the spirit of this invention, they are intended to be included within the scope of the appended claims.

What is claimed is:

1. An enclosed tank having a metal shell with a metal bottom, a metal wall and a metal roof, the bottom and wall each having a layer of insulation applied thereto and the roof comprising a noninsulated metal plate supported upon the top edges of the wall, and an insulated fixedposition ceiling suspended by means attached to the inside of the roof, said ceiling conforming about its periphery to the internal horizontal configuration of the tank at the ceiling location and being suspended in the tank above the intended full capacity level of the tank.

2. A tank yaccording to claim 1 in which the insulated ceiling is substantially planar and horizontally positioned in the tank With the ceiling periphery adjacent the wall and the ceiling insulation is of about uniform thickness throughout its area.

3. An enclosed cylindrical tank having -a metal shell with a metal bottom, a metal wall and a metal roof, the entire bottom and Wall each having insulation applied to the outside thereof and the roof comprising a noninsulated metal plate supported upon the top edges of the wall, and an insulated fixed-position ceiling suspended by a plurality of spaced-apart elongated members attached to the inside of the roof and the ceiling, said ceiling conforming about its periphery to the internal horizontal conguration of the tank at the ceiling location and being suspended in the tank above the intended full capacity level of the tank.

4. A tank according to claim 3 in which the insulated ceiling is substantially planar and horizontally positioned in the tank in contact with the cylindrical wall and the ceiling insulation extends throughout its area.

5. A tank according to claim 3 in which the elongated members by which the ceiling is suspended are vertical and are attached to raftrer means secured to the inside of the roof to distribute the ceiling load over a substantial area of the roof extending around the location of attachment of the elongated vertical members to the rafter means.

6. An enclosed cylindrical tank for storing a refrigerated liquid at a pressure slightly higher than atmospheric pressure, said tank having a metal shell with a metal bottom, a metal Wall and a metal roof supported upon the top edges of the wall, the: entire bottom and wall each having insulation applied thereon to reduce heat-leak adequately to efficiently store a refrigerated liquid in the tank, and an insulated tixed-position ceiling suspended by a plurality of spaced-apart elongated members attached to the inside of the roof and the ceiling, said ceiling conforming about its periphery to the internal horizontal configuration of the tank at the ceiling location and being the intended full capacity level of the tank.

7. A tank according yto claim 6 in which the roof is noninsulated and the insulated Wall extends above the level at which the ceiling edge meets the Wall thereby providing a controlled temperature gradient between the roof and the tank wall to control heat-leak into the tank contents through the extended metal wall.

8. An enclosed cylindrical tank having a metal shell with a metal bottom, Ia metal Wall and a metal roof, the bottom and wal-l each being insulated to retard heat transfer therethrough, the roof comprising a metal plate supported upon the top edges of the wall and at least inin the tank, and an insulated 'fixed-position ceiling suspended by a plurality of spaced-apart elongated members attached by load-distributing means to the inside of the roof and also attached to the ceiling, said load-distributing means comprising a plurality of rafters secured to the inside ofthe roof and following the roof contour, and a plurality of connecting beams which extend across and are connected to the rafters and to which the elongated members are connected at spaced-apart locations, said ceiling conforming about its periphery to the internal wall configuration of the tank at the ceiling location and being suspended in the tank above the intended full liquid level of the tank.

9. A tank according to claim 1 in which the ceiling comprises a plurality of parallel spaced-apart joists supported by the suspending means attached to the roof, bridging between the joists to stiifen them against movement, sheet decking secured to the top of the joists to complete an insulation supporting platform and insulation on the platform of a thickness adequate to retard heatleak enough for practical storage of a refrigerated liquid in the tank.

10. An enclosed cylindrical tank for storing a refrigerated liquid at a pressure slightly higher than atmospheric pressure, said tank having a metal shell with a metal bottoni, a -rnetal wall and a domed metal roof, the entire bottom and wall each having suicient insulation to reduce lheat-leak enough to practically store a refrigerated liquid in the tank, the domed roof comprising a metal plate supported upon the top edges of the wall and insufliciently insulated if at all to suitably store a refrigerated liquid in the tank, and an insulated fixed-position ceiling suspended by a plurality of spaced-apart elongated members attached by load-distributing means to the inside of the roof and also attached to the ceiling, said loaddistributing means comprising a plurality of ra-dial rafters secured to the inside of the roof and following the roof contour, and a plurality of connecting beams which extend across and are connected to the rafters and to which the elongated members are connected at spaced-apart locations, the ceiling comprising a plurality of radially spaced-apart joists supported by the elongated suspending members, bridging between the joists to stifl'en them against movement, sheet decking secured to the top of the joists to complete an insulation supporting platform and insulation on the platform of a thickness adequate to retard heat-leak enough for suitable storage of a refrigerated liquid in the tank, said ceiling conforming about its periphery to the internal wall circumference of the tank at the ceiling location and being suspended in the tank above the intended full liquid capacity level of the tank.

11. A tank according to claim 10 in which transmitting V-means are provided for ow of gas or vapor from below to above the ceiling, and from above the ceiling to below the ceiling.

12. A tank according to claim 10 for storage of a refrigerated liquid cryogen in which the roof is made of a metal normally unsuitable for refrigerated temperatures involved in cryogenic storage.

13. A tank according t-o claim 1in which the insulated Wall extends above the level at which the ceiling edge meets the wall thereby providing a controlled temperature gradient between the roof and the tank wall to control heat transfer to or from the tank contents.

14. An enclosed tank having a metal shell with a metal bottom, a metal Wall and a metal roof, the botto-m and' wall each having a layer of insulation applied thereto and the roof comprising a moninsulated metal plate supported upon the top edges of the wall, and an insulated fixed-position ceiling suspended from the inside of the roof and conforming about its periphery to the internal horizontal configuration of the tank at the ceiling location and being suspended in the tank above the intended full capacity level of the tank, said ceiling including a continuous layer of substantially flat sheet metal having a compression member joined thereto near about its periphery.

15. An enclosed tank for storing a refrigerated liquid, said tank having a metal shell with a metal bottom, a metal wall and a metal roof supported upon the top edges of the wall, the bottom and wall each having insulation applied thereto and an insulated fixed-position ceiling; suspended from the inside of the roof and conforming about its periphery to the internal horizontal configuration of the tank at the ceilingv location and being sus- Y pended in the tank above the intended full capacity leveli of the tank, said ceiling including a continuous layer of substantially flat sheet metal having a compression member joined thereto near about its periphery.

16. An enclosed tank for storing a cryogenic liquid, said tank having a metal shell with a metal bottom, a metal wall and a metal roof, the bottom and wall each having insulation applied thereto and the roof comprising a noninsulated metal plate supported upon the top edges of said wall, and an insulated fixed-position ceiling suspended from the inside of the roof and conforming about its periphery to the internal horizontal conguration of the tank at the ceiling location and being suspended in the tank above the intended full capacity level of the tank, said ceiling including a continuous layer of substantially liat sheet metal having a compression ring member joined thereto near the periphery of the ceiling, a second ring member joined to the sheet metal layerand positioned concentrically thereto and to the compression ring and inwardly from the compression ring to further support the sheet metal layer, and suspension means suspending the ceiling from the roof comprising tension members joined to the rings and to supporting means on the inside of the roof.

17. An enclosed tank for storing a cryogenic liquid, said tank having a metal shell with a metal bottom, a metal wall and a metal roof supported on the top edges of the wall, the bottom and wall each having a layer of insulation applied thereto and an insulated fixed-position ceiling suspended from the inside of the roof and conforming about its periphery to the internal horizontal configuration of the tank at the ceiling location and being suspended in the tank above the intended full capacity level of the tank.

References Cited UNITED STATES PATENTS 1,088,194 2/1914 Whitton 220-9 2,323,297 7/1943 Collins 2205-9 2,980,279 4/ 1961 Lueders 2'20-9 3,225,955 12/1965 Farkas et al. 220-9 3,249,251 5/1966 Nachshen 220--18 DONALD F. NORTON, Primary Examiner.

JAMES R. GARRETT, Assistant Examiner. 

1. AN ENCLOSED TANK HAVING A METAL SHELL WITH A METAL BOTTOM, A METAL WALL AND A METAL ROOF, THE BOTTOM AND WALL EACH HAVING A LAYER OF INSULATION APPLIED THERETO AND THE ROOF COMPRISING A NONINSULATED METAL PLATE SUPPORTED UPON THE TOP EDGES OF THE WALL, AND AN INSULATED FIXEDPOSITION CEILING SUSPENDED BY MEANS ATTACHED TO THE INSIDE OF THE ROOF, SAID CEILING CONFORMING ABOUT ITS PERIPHERY TO THE INTERNAL HORIZONTAL CONFIGURATION OF THE TANK AT THE CEILING LOCATION AND BEING SUSPENDED IN THE TANK ABOVE THE INTENDED FULL CAPACITY LEVEL OF THE TANK. 